The invention relates to improvements in flexible plastic zippers of the type having continuous interlocking ribs and grooves thereon, and more particularly to an improved slider structure and a method of closing heavy duty fastener strips which have three or more rib and groove elements thereon.
In flexible fastener strips of the type that are formed of plastic manufactured by continuously being extruded from a die, the rib and groove elements are matingly shaped so as to interlock when pressed together in a direction normal to the lock. In applying a closing pressure, the strips are pressed together either between a thumb and forefinger or by a slider which is moved along the strips. The ribs and grooves are forced to interlock in position as the normal pressure is applied, with the rib forcing the groove open as it is pushed into it and deflecting its sides sideways until the groove formed between the ribs opens far enough to admit the opposing rib and then interlocks in the grooves.
On heavy duty strips of the type which have three or more tracks, closure cannot be accomplished without considerable effort because the lateral deflection cannot occur. In other words, as ribs are pressed into the grooves on a heavy duty strip having three ribs and three grooves, the ribs forming the sides of the groove cannot push apart, but instead will fight each other. As the ribs on each side of one of the grooves spread apart, the one rib in the middle will move over further onto the other groove so that it reduces the size of the groove. In order to successfully close the fastener, the ribs must spread so that each of the grooves is made wider to admit the ribs of the opposing strip. While this is possible on a two track fastener, it is not possible on a three or more track fastener. Thus, it has been found to be considerably impractical to attempt to close a heavy duty fastener with three or more tracks, due to the fact that the strips fight each other so that when the sides of the groove tend to spread for one groove, one of the sides closes the other groove, instead of opening it. This problem is further aggravated when the fastener being closed is constrained by the sides of the slider that is closing it. Added to the problem described above is the friction of the extra substantial surface of the plastic that is being forced into the interlocking mode. This can be overcome in part by putting a coating of silicone on the zipper track. However, while this permits the slider to move more easily, it does not accommodate the problem of affording more space for the heads and teeth to bypass each other and to snap into position.
In accordance with the principles of the present invention, a method is employed wherein the different ribs and grooves of each of the tracks are closed progressively, one after another, so that each one has enough room to interlock before the next one to it is required to respond in the same way. In accordance with the principles of the invention, this is accomplished by a structure that provides for an angled indentation or for welding an angle bar either on the top or bottom of the inside slider surface between the end of the slider and the separating bridge. The angled bar successively deforms and interlocks the rib and grooves one after the other from one side to the other side of each of the strips.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for the closing of a heavy duty plastic strip having three tracks or more thereon.
A further object of the present invention is to provide an improved closure method and structure for closing heavy duty plastic zippers on the order of those which measure in thickness from between 175 mils to 300 mils or more when interlocked.
A further object of the invention is to provide an improved slider construction which is capable of accomplishing the closing of heavy duty strips having interlocking rib and groove elements thereon wherein the structure of the slider is simplified so that it can be easily manufactured and can be easily adapted or installed, and is capable of long wear and does not require extremely close manufacturing tolerances.
Other objects, advantages and features, as well as equivalent structures and methods which are intended to be covered herein, will become more apparent with the teaching of the principles of the present invention in connection with the disclosure of the preferred embodiment in the specification, claims and drawings, in which: